Flame photometer atomizer burner assembly



Nov. 4, 1958 Y F. G. KEYES 2,858,729

FLAME PHOTOMETER ATOMIZER BURNER ASSEMBLY Filed May 10, 1955 I20 AT usFig.|

INVENTOR. FREDERICK G. KEYES 4 ATTORNEYS .half that of air.

"the burner surface or to blow out entirely.

'case the apparatus will not perform properly.

FLAME PHOTOMETER ATOMIZER BURNER ASSEMBLY Frederick G. Keyes, Cambridge,Mass.

Application May 10, 1955, Serial No. 507,247

4 Claims. (Cl. 88-14) The subject invention relates to anatomizer-burner assembly for use with spectrophotometric apparatus and IUnited States Patent in particular to a burner which will produce a veryfine spray of uniform minute droplets together with a stable flame.

While flame photometry has long been a useful tool in chemical analysiswork it has become increasingly important in recent years particularlyfor analyses of sodium, potassium and calcium from'blood samples. Theresults obtainable with photometric analysis havebecome increasinglyaccurate and considerable effort has been spent in obtainingconsistently reproducible results utilizing relatively small samples ofmaterials.

While considerable attention has been paid to the type of atomizerutilized in these devices, relatively little attention has been paid tothe droplet stream after ithas been produced. In fact, many of theatomizing nozzles encourage the production of a turbulent mist ofparticles in which there is considerable tendency for the particles tocollide and thereby form larger particles. However, in order to obtainuniform reproducibleresults in a flame photometer it is essential thatthe mist which is projected into the flame be made up of a uniform veryfine particle structure. Where large droplets appear in the aerosolcontaining, for example, sodium or potassium the large droplet will tendto produce a pin-point or flash of light which distorts the readings.

It is also highly desirable that the supply of combustible gas beunvaryingly uniform and reproducible from day to day. The most commonlyused flow regulator for this purpose is a light ball floating in atapered cylinder, and while this apparatus is satisfactory for use withsome gases it is unstable when used with hydrogen and readings based onit are unreliable. Hydrogen is about 14.5 times lighter than air but hasa viscosity coeflicient about As a result its kinematic viscosity isover 7 times that of air. When hydrogenpasses through a conventionalball float meter the ball tends to oscillate vertically and horizontallyand the flow rate cannot be read or'reproduced accurately.

While hydrogen is generally a satisfactory and conven tional fuel forphotometric use it may be desirable in certain instances (e. g. toobtain a higher temperature flame) to utilize a slow burning gas. Insuch cases the use of the conventional hydrogen burner tip isunsatisfactory because the flame tends either to blow'away from Ineither It is therefore the object of this invention to provide animproved atomizer-burner assembly for flame photometry apparatus whichprovides greatly improved particle size uniformity and which enclosesthe flame in an annular sheath of particles'in air or oxygen.

-It is a further object of this invention to provide such a burner inwhich the visible portion of the flame is stable and of a uniformbrilliance utilizing either hydrogen or slower burning media.

It is a feature of this invention that it establishes. a-

uniform laminar flow of atomized particles in which there is a minimizedtendency for the particles to collide, but at the same time providesmeans for trapping the larger particles and preventing their passageinto the flame. It is a further feature of this invention that theentrained particles tend to collect and are so directed after separationfrom the air stream that they either return to the sample bottle therebyreducing the total amount of sample needed or alternatively arere-atomized into the droplet stream. It is a further feature of thisapparatus that it provides metering means to supply a constant uniformflow of fuel and also provides an alternative burner assembly which willassure a uniform stable flame when acetylene or propane is used.

This apparatus will be better understood by reference to the drawings inwhich Fig. 1 represents a vertical cross-section through theatomizer-burner and flow meter assembly,

Fig. 2 is a cross-section of the upper taken through the section 2-2 ofFig. 1,

Fig. 3 is a detail drawing of the stable flow regulating float and aportion of the associated tapered cylinder,

Fig. 4 is an enlarged detail showing the edge of the float and theadjacent wall, and

Fig. 5 is a sectional elevation of an alternate burner configuration.

As illustrated in Fig. l, the inlet nipple 10 connects with the oxygensupply which is forced out of the atomizer nozzle 12 under pressure.Coaxial with the nozzle opening is thecapillary supply tube 14. Both thenipple and the capillary tube are supported by the atomizer tube 16which is press fitted to the sealing plug 18 enclosing the bottom of thefirst entrainment chamber 20. This entrainment chamber is formed by atubular outer shell 22 surrounding a pear-shaped baflle 24. The plug 18which is fitted to the lower end of the cylinder 22 carries in its uppersurface a circumferential channel 26. A return tube 28 carries excessmaterial trapped in the entrainment chamber back to the sample holder30.

A connector block 32 carries the cylindrical projecting flange 34 towhich the upper end of the cylinder 22is fitted. The baffle tapers to aplug at it upper end which is fitted to a hole in the block 32. Thehydrogen inlet orifice 36 leads from the fuel supply regulator 60 to bedescribed later, to a fuel supply tube 38 which extends upward along thesame axis as the lower cylindrica chamber 20. I

The connector 32 carries a number of ducts 40connecting the lowerchamber 20 with an upper chamber 42. These ducts may be seen moreclearly by reference to Fig. 2. The upper chamber 42 is formed of vanouter cylindrical shell 44 which is coaxial with the lower shell 22 andlike the lower shell is supported by the member 32. The upper end ofthis chamber is closed by the annular plug 46 and the direction of flowthrough the flow chamber upper chamber is reversed twice through theconcentric' cylindrical baflies 48 and 50. The cylindrical baflle 48 isclosed at its lower end by the plug 52 which is fitted around the supplytube 38 in order to support the bafile. Similarly, the tube 50 isfriction fitted to the annular hole in the plug 46 closing the upper endof tube 44.

In the operation of this device, oxygen is forced in through the nipple10 and passing at high velocity through the deflected streamlines as theatomized mist is first turned to a horizontal direction and then turnedby the wall 22 back to a vertical direction. However, the heavierdroplets tend to be carried by their inertia into contact with thedeflecting members 24' and 22. The particles which impinge upon thepear-shaped baffle 24 either re-evaporate or tendto collect together atthe bottom of this baffle directly over the nozzle 12; If sufiicientmaterial collects in this manner to form a dropletwhich drops back intothe nozzle it will experience the impact of the gaseous atomizing fluidand be projected back into the aersol stream; Some. droplets which arenot caught by the baflle 24 will either settle out of the stream intothe channel. 26 orv will be thrown against the wall 22- when thestreamlinedaerosol is deflected upward again.

Themist which nowconsists of uniformly small droplets passes thenthrough the ducts 413 up back and up again. through the long'reflexchamber 42 to the upper end of the fuel inlet tube 38 where the flame isformed. Each reversal of the flow tends to separate out any remainingabnormally large particles since inertia tends to carry them intocontact with any deflecting surface. The final stream of oxygenuniformly laden with spectrally active particles flows in an annularstream upward around the fuel inlet tube out into and around the flame.The fuel is therefore supplied with oxygen containing a uniform aerosolof the sample at its outer surface and the result is a steadyluminescence.

The hydrogen flow regulator 61) is composed of a vertically disposedtapered tube 62 containing a threaded cylindrical float 64. The upperend of the tube is fitted to the connecting block 66 which in turn isfitted to the fuel inlet orifice 36. The lower end of the tube 62 isfitted to the block 68 having an inlet 70 from the hydrogen supply and avalving means 72 to control the supply. The connector block 68 containsan inner shoulder 74 which supports the lower end of the tube andextends inward to support the float 64 when the flow is shut off. Thetube 62 is slightly tapered on the inside to form a funnel of increasingdiameter as the float rises so that the annular. space between the float64 and the wall of the tube 62 increases as the flow forces raise thefloat.

The structure of the float itself is shown in more detail in Figs. 3 and4. It will be seen that the float is composed of a cylinder having alength somewhat more than twice its diameter, and that each of the fourspiral grooves 78, 80, 82, and 84 are cut around the surface of thiscylinder in the form of a. helix. These grooves are relatively shallowand the resulting structure produces a plurality of helical landsindicated at 86 in Fig. 4 which extend upward around the surface of thefloat. The eifect of these lands is to cause a stabilizing pressure dropin the narrow orifice between the outer periphery of the land and theinner surface of the tube in comparison with the pressure in thechambers formed by the channels. This pressure drop is a function of thespace between the land and the tube wall, and if the float moves closerto one wall than .the other,.the flow and therefore the pressure dropwill be cut. down by the narrower spacing. The resulting relativepressure rise will force the float back to the center of the tube. Inaddition, the spiral nature of these lands forces the float 64 to turnas the gas flows up around it. The flow is primarily across the landsurface not in the groove and therefore the float will turn in acounterclockwise direction when viewed from below along the line of flowof the gase. This turning motion has an additional inertial stabilizingeffect upon the float and improves the aerodynamic pressurestabilization.

When it is desirable to use this flame photometer with a V supply offuel having a relatively low burning velocity, the

alternative burner assembly shown in Fig. will be preferable-toreplacethe fuelsupply tube 33. The burner assembly. itself whichreplaces the supply line 38 of Fig. l, is considerably more complicatedthan the simple tube used with hydrogen.

Only. the burnerv itself. is shown, and. it Willbeunderstood that likethe simple tube 38, this burner is surrounded by the three coaxial tubesor shells shown in Fig. 1 as 44, 48, and 50. As in that figure, anannular stream of aerosol passes up around the burner and into andaround the flame.

The hydrocarbon burner. tip is supported by a. base member 100. whichcarries on its bottomsurface the projecting supply tube 102 which, likethe supply tube 38 of Fig. 1, carries the combustible gas to the burner.The orifice 104 connects this tube with the mixing chamber for the fueland. aerosol; Mounted on the upper surface of the cylindrical basemember are three coaxial cylindrical sleeves of decreasing. diameter;and length 110, 112, and 114. Sleeve 112 carries the plug 118 at itsend. This plug supports the inner burner tip 120 and in addition ispierced by a plurlity of holes 122 around this inner burner tip 120.The. lower endv of. this sleeve 112, is perforated by a plurality ofopenings 124. It will be noted that there. is a gap between the end ofthe inner cylinder 114 and the plug 118. In addition there is an annularchamberor passageway formed between cylinders and112 and another.passageway between sleeves 114 and 112. The holes 124 serve to connectthese two passageways.

The burner base 100 also carries a plurality of radial passages 130which supply oxygen of air carrying sample particles. to the cylindricalcavity formed by the inner sleeve 114.

The hydrocarbon burner functions as follows. Fuel under pressure issupplied through the supply line 102 and throughthe orifice 104 to themixing chamber inside the tube or, sleeve 114. The aerosol mist is drawnthrough the radial openings 130 and mixes with the fuel to form acombustible mixture which passes up the tube 114. Most of thecombustible mixture passes out through the burner tip where it isignited forming a flame. However a relatively small portion of thecombustible gases passes out through the smaller passages 122 in theplug 118. These passages are arranged around the burner tip 120 and forma plurality of small pilot flames which tend to keep the main flame atthe burner tip ignited around the periphery of its base. As anadditional safety factor a small portion of this combustible mixturepasses back down through the annular passage outside of the sleeve 114and through the ports 124. This supply of gas emerges through theannular opening between the end of the sleeve 112 and the shieldingsleeve 110 where it is ignited forming an-annular ring of flame.

The effect is of a double pilot light in which the small annular ring offlame keeps each of the inner pilot lights lit and these flames in turnassure a stable combustion at the tip of the burner 120. It has beenfound that this arrangement effectively overcomes the tendency of anyhydrocarbon fuels to burn away from the base and in some instances toblow out entirely. As specified above, this burner is the equivalent forhydrocarbons of the simple tube 38 of Fig. 1. As in the apparatus ofFig. 1, an annular stream of aerosol would flow upward aroundthe sleeve1'10 and provide a uniformly luminescent sheath at the outer surface ofthe flame.

While this. development has been described by reference to a singleembodiment, it will be understood that alternative constructions wouldbe possible without departing from the invention as encompassed withinthe following claims;

I claim:

1. In a flame photometer, an atomizer burner assembly comprising asample container, a suction tube from the container and a. coaxialoxygen tube forming a vertically disposed atomizer assembly, aseparation chamber having a streamlined baifle member in line with. andabove the; atomizer tubes surrounded by a coaxially disposed cylindricalshell, return means to the. sample container. from the separationchamber, a flow reflex chamher formed by a plurality of concentricallydisposed vertical cylinders, a connecting member having ports betweenthe two. chambers, and burner inlet means vertically disposed along theaxis of the flow reflex chamber.

2. In a spectrophotometric apparatus an atomizing burner assemblycomprising an atomizer assembly directing a stream of dropletsvertically upward, a droplet entraining chamber having a spheroidalbaffle disposed in the path of the stream deflecting the stream towardthe horizontal, a chamber wall vertically disposed in the path of thedeflected stream concentric with the periphery of the baflle forming avertically disposed annular passage, means for producing laminar dropletflow, and a burner for the droplet stream.

3. In a flame photometer an atomizer-burner assembly comprising acentrally disposed connecting block perforated by a ring of verticallydisposed ports connecting its upper and lower faces, a lower cylindricalshell projecting from the lower face of the support outside the ring ofports, a streamlined baffle projecting from the lower face of thesupport and centrally disposed within the lower shell, an annular plugto close the end of the lower shell, a vertically disposed atomizerassembly fitted to the hole in the plug and directing a droplet streamvertically against the bottom of the baflle, sample supply means to theatomizer, oxygen supply means for the atomizer, a fuel supply tubeprojecting vertically from the center of the ring of ports in theconnector block, a supply duct in the block leading to this tube, anupper cylindrical shell fitted to the upper face of the connector blockand surrounding the ring of ports, an annular plug closing the upper endof said shell, a second shorter shell coaxial with and inside the first,means for supporting the second shell at its base so that it clears thelower side of the annular plug and a third shell inside and coaxial withthe second shell, fitted to the hole in the plug, and surrounding thefuel supply tube, said shells forming a flow reflex chamber.

4. A spectrophotometric burner apparatus comprising a body having wallsdefining a chamber, a sample container communicating with the chamberand having an atomizer to inject an aerosol mist ofthe sample into saidchamber, spheroidal baffle means within said chamber for deflecting saidaerosol mist to separate out oversized par-' ticles, a connector blockhaving a series of vertically disposed ports associated with the upperend of said cham ber, vertically disposed fuel supply means within andextending above said connector block, regulating means for said fuelsupply means, and a plurality of vertically disposed concentriccylindrical wall members defining a flow reflex chamber to cause a flowof aerosol mist around said fuel supply to produce a luminescent sheathof particles at the surface of the flame.

References Cited in the file of this patent UNITED STATES PATENTS1,889,705 Sherwood Nov. 29, 1932 2,664,779 White Jan. 5, 1954 2,714,833Gilbert Aug. 9, 1955 2,753,753 Gardiner July 10, 1956 FOREIGN PATENTS408,605 Great Britain Apr. 9, 1934 679,452 Germany Aug. 5, 1939 599,190Great Britain Mar. 8, 1948 OTHER REFERENCES Page 250 of Optik, Vol. 10,No. 5, 1953.

